A variety of retractors and dilation systems have been used to provide a traditional “open” or “mini-open” approach to the posterior spine, as well as for providing the more modern “minimally invasive” and “percutaneous” access to the spine. The “open” or “mini-open” approaches to the spine typically require larger incisions. These larger incisions readily provide visual and instrument access to the surgical site; however, larger incisions generally result in greater damage to muscle tissue, blood loss, long healing times accompanied by prolonged pain and significant scarring.
The development of minimally invasive, percutaneous procedures has provided a major improvement in reducing recovery time and post operative-pain. In minimally invasive, percutaneous techniques patient trauma is minimized by creating a relatively smaller incision, followed by the introduction of a series of successfully larger dilators installed in sequence to dilate the soft tissues and increase the effective size of the incision. In some cases, a guide wire is used to first access the surgical site and then cannulated dilators are installed over the wire. Following installation of the largest dilator deemed necessary, a cannula or retractor is advanced over the largest dilator for providing a working channel from the skin of the patient to the working space adjacent to the spine. Surgery is performed or an implant is inserted through a surgical port or cannula inserted into the dilated incision.
Instead of cutting a larger opening, sequential dilation splits the surrounding tissue to create a larger opening. Splitting the muscle fibers apart, rather than cutting the muscle causes less damage to the tissue and leads to faster recovery times and reduced patient discomfort. Also, sequential dilation provides an advantage in that it allows the surgeon to make an initially small incision, then gradually increase the size of the opening to the minimum size required for performing the surgical procedure, thus reducing tissue damage and speeding patient recovery time.
Certain spinal procedures, such as those developed by VertiFlex, Inc. and described in U.S. patent application Ser. No. 11/314,712 entitled “Systems and methods for posterior dynamic stabilization of the spine” filed on Dec. 20, 2005 and U.S. patent application Ser. No. 11/582,874 entitled “Minimally invasive tooling for delivery of interspinous spacer” filed on Oct. 18, 2006 and U.S. patent application Ser. No. 11/593,995 entitled “Systems and methods for posterior dynamic stabilization of the spine” filed on Nov. 7, 2006, U.S. patent application Ser. No. 12/148,104 entitled “Interspinous spacer” filed on Apr. 16, 2008, U.S. patent application Ser. No. 12/217,662 entitled “Interspinous spacer” filed on Jul. 8, 2008, U.S. patent application Ser. No. 12/220,427 entitled “Interspinous spacer” filed on Jul. 24, 2008, U.S. patent application Ser. No. 12/205,511 entitled “Interspinous spacer” filed on Sep. 5, 2008, U.S. patent application Ser. No. 12/338,793 entitled “Interspinous spacer” filed on Dec. 18, 2008, U.S. patent application Ser. No. 12/354,517 entitled “Interspinous spacer” filed on Jan. 15, 2009, all of which are incorporated herein by reference in their entireties, access the surgical site through tissue and through the supraspinous ligament, for example, for the insertion of a device, such as an interspinous spacer. Whereas the procedure may be performed in an open, mini-open or minimally invasive, percutaneous approach, penetrating the supraspinous ligament can be challenging as the ligamentous tissue is not only strong but also slippery. However, penetrating the supraspinous ligament particularly lends itself well to sequential dilation as the ligament is formed of a cord of substantially uniformly oriented fibrous strands that are advantageously capable of being split apart rather than transversely cut for minimizing trauma and increasing patient recovery time. Furthermore, approaching the interspinous process space through the supraspinous ligament, like the VertiFlex device, advantageously avoids the multifidus muscle and thereby preserves its critical function as a stabilizer of the lumbar spine. Because of the difficulties associated with penetrating ligament, there is a special need for a dilator and/or dilator system designed for accessing a surgical site through ligament such as the supraspinous or interspinous ligament. The current invention provides a dilator and dilator system for establishing an opening through ligament that may also be used in conjunction with minimally invasive, percutaneous procedures.